Prepping for Installation
34
Building Technologies 125-202
06/06/2017
1,440kW/.001 = 1,440,000
Since 1,440,000 is greater than 65,535, using data scalar 1 returns an incorrect result.
Data scalar 1 is not an appropriate choice.
Reviewing this example using the data scalar 3 value of .1 provides the following
result:
1,440kW/.1 = 14,400
Since 14,400 is less than 65,535, using data scalar 3 is a good choice for this example.
Values Requiring Two Registers
Additionally, some values (for example, kilowatt hours) may cover a dynamic range
that is larger than 65535 and require two Modbus registers. Any parameter in the
Modbus Register Assignment tables that shows two registers (identified by the terms
MSW (Most Significant Word) and LSW (Least Significant Word)) are examples of this
wide-ranging parameter.
To interpret the values contained in these registers, the steps are:
1. Multiply the MSW register by 65536.
2. Add the result to the value found in the corresponding LSW register.
3. Multiply the result by the appropriate scalar value from Table 8.
For example, assume that System Total True Energy (kWh) is desired and the value of
5013 is read from register 44001 (LSW), and 13 is read from register 44002 (MSW)
and that the register 44602 data scalar is set to 3.
To calculate the total kWh recorded:
1. Multiply the MSW by 65536: 13 x 65536 = 851968
2. Add the LSW: 851968 + 5013 = 856981
3. Multiply by the scalar 3 value of 0.1: 856981 x 0.1 = 85698.1 kWh
When reading two register values, ViewPoint automatically calculates the total value.
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